In the basic and clinical research on brain's response to injury, cortical electrical signals from the brain, namely EEG, may be useful in providing an immediate indication of the dysfunction. As such, we hypothesize that quantitative EEG would be a powerful tool for basic research on brain injury and, eventually, clinical diagnosis. A novel approach to analyzing brain's early response to injury, based on the method of "multiresolution wavelet entropy (MRWE)" is proposed. Since the recovery of brain rhythms in response to injury occurs in different stages involving transition of rhythmic activities in different frequency bands, we propose to monitor and quantify the variations in entropy that occur within each clinical band. We hypothesize that a) following global ischemic brain injury, the time domain entropy of EEG would form a sensitive indicator of the level of injury and that the MRWE of EEG in each clinical band would identify features related to the bursting characteristics of EEG in the immediate post-ischemic recovery periods, and b) the corresponding entropy measure derived from the cortical field potentials would have cellular origins (firing pattern of neurons) in cortical and subcortical areas of the brain. To explore these hypotheses and to develop rigorous theoretical tools for experimental studies on brain injury, we propose: 1: Theory - a) Derive a time domain entropy measure with a view to monitor the progress of recovery of EEG following global ischemic brain injury. b) Derive an MRWE-based segmentation procedure to identify the characteristics of initial bursting EEG, seen during early phases of post-ischemic recovery. 2: Experiments - Using experimental single and multi-unit recording by the microelectrode method, show that the varying levels of MRWE derived from the cortical field potentials reflect the transitional stages of post-ischemic rhythmic activity of neuronal population in the thalamus and the cortex. The significance of this project primarily lies in developing a novel quantitative tool that can benefit basic and clinical scientists studying brain injury.